The present invention relates to deepwater drilling and production operations. More particularly, the present invention relates to providing protection from vortex induced vibration ("VIV") to parallel runs of intermittently connected cylindrical elements such as drilling riser control pod hoses bundled with wirelines.
Assemblies of multiple cylindrical elements or lines such as these hoses and associated wirelines run from surface facilities to valve control pods which manage blow out preventors or "BOPs" on the ocean floor. The wireline provides support in deploying, maintaining, and retrieving the control pod hose and clamps interconnect the control pod hose to the wireline at regular intervals along their lengths. The control pod hose itself is a multiplex hose in which many hydraulic and/or electrical control lines are bundled within a single sheath. These control lines manipulate valves in the control pod of the BOP or otherwise control remote, subsea equipment.
Such applications require long runs which are subject to ocean currents. These currents can cause vortexes to shed from the sides of both the hose and the wireline, thereby inducing vibrations that can lead to the failure of either element or the clamps therebetween. Thus there is a need to provide protection from VIV in the control pod/support line assembly.
Helical strakes and the like, e.g., spiral wrapping ropes around the bundle, may be effective to reduce the VIV, but markedly increase current-induced drag. As a consequence, the bundled control pod hoses may be induced to "sail" past the risers and create tangling problems during rulnning and retrieval operations.
By contrast, fairings are effective to control both VIV and drag problems. However, the practice of using fairings such as deployed for VIV protection about single cylindrical elements are not suitable for such tandem or other multiple line assemblies.
An advantage of the fairing of the present invention is that it is suitable for deployment about bundled, i.e., side by side cylinders. Another advantage of the present invention is the ease of fairing installation about the cylinders.